The Research On The Laying Powder System Of Electron Beam 3D Printing And The Process Of Stainless Steel Powder Forming

This paper investigates the metal powder laying system and powder forming process of EB 3D printing. There is a perfect application prospect on the biological medical, aerospace and other fields.The mechanical structure and the embedded control system of EB 3D printing laying powder system are designed in accordance with the requirements for the design of EB 3D printing, and the whole powder system is finished. The mechanical structure is divided into four parts:the supporting table, lifting platform, discharging powder bins and recycling bins, running gear. The embedded control system includes in software and hardware. The corresponding verification tests are conducted in the precision of the lifting platform, the velocity of discharging powder for powder bins and the uniformity of laying powder. Lifting platform dropping precision is　+0.002mm/0.5mm; the velocity of discharging powder is 39.0625-5000mm3/s; When laying a 0.5mm layer of powder, S is 120,which is the ratio of the discharging powder’s velocity to laying powder velocity. The powder is uniform after compaction.The mechanism of "blowing powder" with electron beam in condition of vacuum is analyzed. Compared with the different influence on powder melting of resistance wire heating and deflection and scanning of electron beam, it concluded that the 25 minutes preheating time reduces blowing powder rate to below 10% in compound preheating system which combines the resistance wire heating and deflection and scanning of electron beam,44.4% less than the preheating time of utilizing a single heating method. The problem of "blowing powder" can be solved effectively by heating powder 30 minutes in composite preheating system.Powder melt forming process parameters with EB 3D printing has a direct effect on the surface morphology of 316L stainless steel forming sample. In the case of constant parameters, accelerating voltage U, scanning distance L and so on, the surface morphology and the surface roughness of samples with the same I/F value which is the ratio of electron beam I to scanning frequency F are similar. With the increasing of I/F value, the surface morphology of forming samples transform from reticulation to gap, and the surface roughness of samples increase. In order to ensure powder forming rate beyond 90%, it’s necessary to preheat at least 40s for layers forming in compound preheat system. With powder forming layer by layer and heat accumulating, the hardness of the former layer decreases because of the tempering and annealing effect of the next layer. The samples of EB 3D printing obtain compact structure, small grains. The compactness is 98.12%. Compared first layer and multilayer powder melt forming, it can be found that the mass fraction of manganese (Mn) which is low melting point decrease obviously, the mass fraction of other elements do not change significantly.